react native - assigning state to const

Question

I'm starting with react native, and when using a library called react native paper, I've come across a statement where the state is being assigned to a const as shown below.

import * as React from 'react';
import { Searchbar } from 'react-native-paper';

export default class MyComponent extends React.Component {
  state = {
    firstQuery: '',
  };

  render() {
    const { firstQuery } = this.state;
    return (
      <Searchbar
        placeholder="Search"
        onChangeText={query => { this.setState({ firstQuery: query }); }}
        value={firstQuery}
      />
    );
  }
}

Beginning of the 'Render' method, you could see const { firstQuery } = this.state; Could someone please explain why the state is being assigned to a const named 'firstQuery', and even if it have a reason, how will the assignment correctly map the property 'firstQuery' inside the state object to the const ?

Thanks in advance. The code sample is from https://callstack.github.io/react-native-paper/searchbar.html#value

Answer 1

That syntax is not React nor React Native. It's just Javascript's syntax, called destructuring.

const { firstQuery } = this.state;

is equivalent to

const firstQuery = this.state.firstQuery;

just a short-hand shortcut syntax, you see 2 firstQuerys? People just don't want duplication in code, so they invented it.

---

See the vanilla javascript snippet below:

const object = {
  name: 'Aby',
  age: 100,
}

const { name, age } = object;
// instead of 
// const name = object.name;

console.log(name, age);
console.log(object.name, object.age);

//=========================================
// imagine:
const obj = {
  veryLongPropertyNameToType: 420
}

const { veryLongPropertyNameToType } = obj;
// instead of
// const veryLongPropertyNameToType = obj.veryLongPropertyNameToType;